Most semiconductor devices made today, including optoelectronic devices such as light emitting devices, solid state lasers, power electronic devices, and on-chip microsystems integrating optical and electronic devices are fabricated using compound semiconductors including, for example, gallium nitride (GaN), gallium arsenide (GaAs), indium phosphide (InP), and related materials. Related materials used in such fabrication include, for example, indium gallium nitride (InGaN), aluminum gallium nitride (AlGaN), Mg-doped GaN, Si-doped GaN, an InAlGaN alloy, indium gallium arsenide (InGaAs), aluminum gallium arsenide (AlGaAs), an InAlGaAs alloy, aluminum indium phosphide (AlInP), aluminum gallium indium phosphide (AlInGaP), and the like. Due to the lack of cost effective, high quality single crystal bulk substrates of the same material, for example, a bulk GaN substrate, an overwhelming majority of these devices use bulk substrates of dissimilar materials such as sapphire (Al2O3), silicon carbide (SiC), and silicon (Si).
However, differences in crystallographic, thermal and chemical properties between a device and dissimilar substrate material often results in high defect density in the device film that ultimately compromises the performance of the semiconductor device. These defects are frequently in the form of, for example, dislocations, vacancies, substitutions, twins, voids, strain-related three-dimensional (3D) growth islands, and excessive surface roughness due to strain relaxation.
C-axis oriented, epitaxial GaN device films, for example, have been grown on a (111) plane of silicon substrates. As used herein, the (111) plane refers to a plane having indices (111) used in a Miller index notation system in crystallography for orientation of planes in crystal lattices. In the cubic crystal lattice of silicon that is defined by three perpendicular lattice axes, this plane intercepts one unit on each of the lattice axes, that is, a plane formed by three diagonal corner points of the lattice. However, because of the high mismatch in lattice parameter and coefficient of thermal expansion (CTE), as well as due to a chemical reaction between gallium and silicon, an aluminum nitride (AlN) nucleation film on silicon is usually required before the deposition of GaN. Even with the AlN nucleation film, GaN films can still have defect counts as high as 109/cm2. This high defect count is one of the key issues preventing a wider use of silicon as a substrate for group III nitride semiconductor devices. The adoption of silicon substrates will accelerate the integration of electronic and photonic devices by taking advantage of conventional complementary metal-oxide-semiconductor (CMOS) manufacturing technologies and supply chains. Accordingly, there is a need for overcoming the defectivity issues in group III nitride films on silicon or silicon based substrates.
Hence, there is a long felt but unresolved need for methods and semiconductor devices that incorporate defect mitigation structures for overcoming the defectivity issues related to group III nitride devices on silicon based substrates.